Feline immunodeficiency virus (FIV) produces a pathological condition in cats similar to AIDS in humans, produced by-human immunodeficiency virus (HIV). Therefore, FIV is a useful animal model for studying AIDS. The Crandell feline kidney (CrFK) tissue culture cell line can be productively infected with FIV. Virions from infected CRFK cells were isolated, the genomic RNA purified and a CDNA library constructed. A series of overlapping clones, representing at least 6Kbp of the 9Kbp genome, have been isolated. FIV CDNA clones hybridize only to RNA and DNA from infected CRFK cells, thus ruling out that endogenous retroviruses have been induced. Partial sequence analysis of some clones resulted in a sequence which does not correspond to any retroviral sequences present in GenBank. This result suggests that, like its human counterpart, HIV, the feline immunodeficiency virus may contain additional open reading frames relevant to its pathology.